1. Technical Field of the Invention
The present invention relates to an electrochromic or photoelectrochromic device, particularly suitable for reversible storage and display of data and for the control of light transmission, making use of one or two electrodes made of semiconductor having high specific surface area.
2. Brief Description of the Related Art
In order to prepare an electrochromic device in which the changing of visible light absorption is greater than 90% (for example from 5 to 95%), and which uses molecules as electrochromic units, it is necessary for the surfaces to have densities reaching the value of .GAMMA.0.sup.-8 mol/cm.sup.2 if the extinction coefficient of these molecules varies from .DELTA.IAUX 101 .backslash.f "Symbol"}=20'000 when changing oxidation state. Up to now, this requirement has been met in the following manner when preparing electrochromic devices:
the electrochromic compound is present in solution contacting the electrode. The requirement is fulfilled with a 0.25 M concentration and a layer thickness of the solution of 2 .mu.m;
the electrochromic compound is electrochemically precipitated in a thin layer on an electrode;
the electrochromic compound is polymerised or incorporated into a film of polymer or composite material on the surface.